Pressure carburetor



United States Patent 3,174,739 PRESSURE CARBURETQR Edward J. Barr,Torrance, Calif, assignor to McCulloch Corporation, Los Angeles, Caiifi,a corporation of Wisconsin Filed Feb. 12, 1962, Ser. No. 172,519 4Claims. (Cl. 261-65) This invention relates to fuel feeding systems forinternal combustion engines and the like, and relates more particularlyto devices or systems in which the liquid fuel is supplied thereto undersuper-atmospheric pressure.

While the invention has particular utility in connection with two-cycleinternal combustion engines, and is disclosed in such connection, it isto be understood that its utility is not confined thereto.

Certain problems and ditliculties are involved in providing a fuelsupply device which maintains a satisfactory fuel-to-air ratio over thefull engine operating range, and it is an object of the presentinvention to provide a fuel supply or charge forming device which willsolve these problems and overcome said diiiiculties.

It is another object of the invention to provide a charge forming devicewhich maintains a satisfactory fuel-to-air ratio over the complete rangeof engine operation.

It is still another object of the invention to provide a charge formingdevice or carburetor of this character wherein the proper fuel-to-airratio is determined by the .of this character wherein the transitionfrom the idling range is smooth and fiat spots are eliminated.

It is still another object of the invention to provide a simplifieddevice of this character which may be built at reasonable cost and whichis capable of accurately regulating the fuel supply to maintain a properfuel-to-air ratio through wide ranges of engine load and speed.

It is a still further object of the invention to provide a device orsystem of this character wherein the fuel is supplied to the nozzle at asubstantially constant superatmospheric pressure and the metering of thefuel is controlled in accordance with pressures at predeterminedlocations in the induction passage.

The characteristics and advantages of the invention are furthersufficiently referred to in connection with the following detaileddescription of the accompanying drawing, which represents oneembodiment. After considering this example, skilled persons willunderstand that many variations may be made without departing from theprinciples disclosed, and I contemplate the employment of anystructures, arrangements, or modes of operation that are properly withinthe scope of the appended claims.

Referring to the drawing, which is for illustrative purposes only, thereis schematically shown a fuel supply system or charge forming deviceembodying the present invention.

Referring more particularly to the drawing, the device comprises a bodyhaving an induction passage which includes a venturi 12 therein.Anterior to the venturi is an air inlet 14 and downstream of saidventuri is a throttle body section which is connected with an air fuelmixing chamber by means of a connecting chamber 20. The end of the bodyhaving the mixing chamber 18 is connected "ice to the crankcase of a twocycle internal combustion engine, not shown.

The body 10 includes a shallow recess 22 defined by a top wall 23 and anannular wall 24 normal to the top wall 23. A flexible diaphragm 25,substantially parallel to the wall 23, closes the open end of the recess22 to thereby define a fuel chamber, said diaphragm being marginallyclamped between the annular wall 24 and the upper end, as shown in thedrawing, of an annular wall 26 of an intermediate plate 2% which has anupper recess 3% and a lower recess 32 separated by a partition Wall 34.Flexible diaphragm 25 serves as a movable wall separating the chamber 22and the chamber 30.

Recess 32 has its open lower end closed by a flexible diaphragm 38 whichis marginally clamped between the lower free end of the annular wall 26and the upper free end of a wall 40 of an outer plate or cap, indicatedgenerally at 42, cap 42 having an upwardly opening recess 44 which isclosed at its upper end by the diaphragm 38 which serves as a movablewall separating the chambers 32 and 44. The intermediate plate 28 andthe cap 42 are secured to the body by any suitable means such as, forexample, screws, not shown.

Diaphragm 25 may be termed a wet diaphragm, since it comprises one wallof the chamber 22 which is a fuel chamber, while diaphragm 38 is a drydiaphragm.

Fuel from a pulse pump is provided by means of a conduit 48 which isconnected to one end of a valve chamber or bore 50, the upper end ofsaid bore or valve chamber having a valve seat 52. Valve chamber or bore50 extends upwardly from the wall 23 of the fuel chamber 22 and slidablydis-posed in said bore 50 is a movable valve member 54 of polygonallyshaped cross-section. The polygonally shaped cross-section of valvemember 54 facilitates flow of liquid fuel along the facets of the valvebody into the fuel chamber 22. There is a cone shaped tip or valveportion 56 at the inner end of the valve member 54 which cooperates withthe valve seat 52 for controlling the flow of fluid from the conduit 48into the fuel chamber 22.

The top of the fuel chamber 22 is provided with an elongated recess 60in which is disposed a pin 61 providing a pivotal support for a levermember 62. Lever member 62 has an inverted U-shaped portion 63 receivingthe pin 61. From one arm of the U-shaped portion 63 there is ahorizontal portion 64, as viewed in the drawing, and an inclined portion65 which is provided with an arcuately shaped end 66 engaging a plate'67 disposed centrally on the upper side of the diaphragm and securedthereto by any suitable well known means. The opposite side of thediaphragm 25 is provided with a plate 68 similarly secured to saiddiaphragm. The upper end of a pin 69 engages the plate 68 and said pinis slidably received in a bore '70 provided therefor in the partition 34of plate 28. The lower end of pin 69 is engaged by a plate 71 secured tothe upper surface of the dry diaphragm 38, there being a plate 72secured to the opposite side of said diaphragm.

Lever 62 has a second horizontal portion '74 which extends beneath thevalve member 54, said valve member having a rounded lower end portion 75operably engaged by the lever portion 74. Body 10 also is provided witha bore 76 which extends upwardly from the top of the fuel chamber 22 andin which is disposed a spring 77 which reacts between the upper end ofthe bore 76 and the horizontal portion 64 of the lever 62 to urge thelever in the clockwise direction on pivot pin 61 and thereby urge thevalve member 54 in the closing direction.

Fuel is supplied to the induction passage of the carburetor from a fueljet or nozzle 80 which is connected with the fuel chamber 22 by means ofa conduit 81. The fuel supplied to the jet 80 through the conduit 81 iscontrolled by a needle valve 82 having an externally V threaded body 83threadably received in a tapped bore 84 in a boss 85 of the body 10. Theinner end of the body 83 of the needle valve isprovided with a coneshaped tip 86 which extends into a portion ofthe conduit 81. The outeror free end of the body 83 is provided with a slotted head 87 wherebythe valve 82 may be turned to move the tip 86 in the conduit 81 andvary' the effective size thereof and thereby determine the quantity offuel delivered to the jet or nozzle 80. There is an air-bleed passage 88in the boss 85 whereby atmospheric air is supplied to the fuel passage81 downstream of the tip 86 of the needle valve 82.

Chambers 30 and 44 are vented to atmosphere by means of passages 90 and91, respectively. The dry chamber 32 above the dry diaphragm isconnected with the induction passage by an air passage 92 and a branchpassage 93 connected to the induction passage at the I throat 94 of theventuri 12.

There is means for modifying the value of the. suction transmitted fromthe venturi throat 94 to the dry diaphragm chamber 32 and said meanscomprises a pair of ports 98 and 99 positioned respectively upstream anddownstream of the trailing edge of a butterfly valve member 100 whensaid valve member is in the closed position. Valve member 100 isoperably mounted on a valve shaft 101 which is connected to any suitablecontrol mechanism, not shown. Parts 98 and 99 are connected to a chamber102 which has a connection 103 with the conduit 92.

There is means for regulating the modifying action on the suction to thechamber 32, said means comprising a needle valve 105 having anexternally threaded body or stem 106 threadably disposed in a tappedopening 107 provided therefor in the body 10. The inner end of the body106 is provided with a cone-shaped tip 108 which extends into thepassage 103 at its point of connection with the chamber 102, said conecooperating with a valve seat 109 provided therefor at the junction ofsaid conduit or passage 103 and the chamber 102. The outer or free endof the valve 105 is provided with a slotted head 110 whereby said valvemay be rotated to vary the position of the tip 108 relative to the valveseat 109 which thereby provides a variable orifice.

The usual reed valve 115 is operably positioned at the outlet of thefuel-air mixing chamber 18.

In operation the pin 70 provides a. connection between the wet and drydiaphragm 25 and 38, respectively, so that suction signals fromtheinduction passage of the carburetor are transmitted from the dry tothe wet diaphragm.

More particularly, whenthe throttle or butterfly valve 100 is at theidling position, as shown in the drawing, there is relatively lowpressure at the discharge side of said throttle valve and substantiallyatmospheric pressure at the upstream or anterior side of said valve.Thus, the suction on port 99 is relatively high with air bleeding intothe air metering system through connections or ports 99 and 93, whichreduces the effective force of the signal transmitted to the chamber 32.

The suction transmitted to the chamber 32 through the air meteringsystem causes a reduction of pressure in said chamber 32 so thatatmospheric pressure in the chamber 44 at the opposite side of diaphragm38 causes said diaphragm to move upwardly and said upward movement istransmitted through the pin 70 to the dry diaphragm 25. Such upwardmovement of the diaphragm 25 forces an additional amount of fuel to thefuel nozzle 80 and simultaneously actuates the lever'62 in acounterclockwise direction to effect proper opening of the fuel valve54.

Upon opening movement of the throttle valve 100 from the idlingposition, the lower edge of said valve reaches a point adjacent port 98which reduces bleeding of air into the signal system through said port,since said port is now at least partially subjected to the lowerpressure or higher suction donwstream of the valve 100. When the loweredge of the valve 1% reaches the above described open position there isa reduction of pressure at the downstream side of said valve and henceon said port 99. Upon opening of the valve the speed of the engine willincrease causing an increase in air flow through the venturi 12 andeffect a lowering of the pressure or increase of the suction on theconduit or passage 93. The net result is an increase in the strength ofthe signal to the chamber 32 and an increase in the amount of fueldischarged by the fuel nozzle in accordance with the amount of air drawnthrough the induction passage, including the mixing chamber 18.

At Wide open throttle there is suction at the ports 98 and 99 and at theentrance to the passage 93. The suc-' tion at the throat 94 of theventuri 12 constitutes the major source of signal strength because ofthe increase in air flow, and hence drop in pressure at the throat ofthe venturi, and the reduction of manifold vacuum at the ports 98 and99. With the throttle in the full open position a signal system isresponsive to the air flow through the induction passage and primarilythrough the throat of the venturi 12.

As the throttle valve moves toward the closed position the pressurestransmitted to the chamber 32 through the ports 98, 99 and the passage93, will occur in the reverse sequence from that hereinabove described.

It has been found that with the foregoing arrangement a suitablefuel-to-air ratio is provided throughout the range of engine operationand the fuel-to-air ratio is pre cisely tailored to the demands of theengine under such conditions.

The invention and many of its attendant advantages will be understoodfrom the foregoing description and it Will be apparent that variouschanges may be made in the form, construction and arrangement of partsof the invention without departing from the spirit and scope thereof orsacrificing its material advantages, the arrange ment hereinbeforedescribed being merely for purposes of illustration.

I claim: I

1. A pressure carburetor comprising: a body having an induction passagetherethrough, said induction passage including an air inlet portion, aventuri receiving air from said air-inlet portion and having a throat ofrestricted diameter, a throttle valve portion, an enlarged air-and fuelmixing chamber at the outlet end of said induction passage said mixingchamber being enlarged relative to the portion of said induction passagecontaining said throttle valve, and a recess; a butterflly throttlevalve in said throttle valve portion; a wet diaphragm closing one sideof said recess to define a fuel chamber, said dia phragm having top andbottom discs secured centrally thereto; a plate having top and bottomrecesses, said plate being attached to said body and marginally securingthe wet diaphragm so that said diaphragm forms a movable wall betweenthe fuel chamber in the body and an atmospheric chamber defined by oneof the recesses in said plate and said diaphragm, a partition in saidplate dividing said chambers therein; a dry diaphragm closing theopposite recess of said plate and defining there- With a variable airpressure chamber; said dry diaphragm having discs secured thereto at thecenter thereof; a cover having a recess therein secured to the plate andmarginally securing the dry diaphragm to said plate, the recess in saidcover being at the opposite side of said variable pressure chamber anddefining an atmospheric chamber; means operably interconnecting saiddiaphragms so that movement of either diaphragm toward the other willeffect corresponding movement of said other diaphragm; said body havinga fuel inlet for fuel under super atmospheric pressure; said inletincluding a valve 7 chamber; a multi-sided fuel valve in said valvechamber, said fuel valve controlling the inflow of fuel to the fuelchamber; a fuel valve control lever pivotally mounted in the fuelchamber and having one end engaging the upper disc of the wet diaphragmand the opposite end operably engaging the fuel valve; spring meansurging the lever in a direction to effect closing movement of the fuelvalve and constituting the sole spring means acting on said fuel valve;means defining a main fuel nozzle for discharging fuel into the enlargedair-and-fuel mixing chamber, said main nozzle being connected with thefuel chamber; variable orifice means including a manually adjustableneedle valve having a tip controlling the fuel flow to the main fuelnozzle; air-bleed passageway means connecting the main nozzle withatmosphere; air signal pressure means comprising passageway means havingone end connected with said air pressure chamber, chamber means, orificemeans providing the sole communication between said chamber means andsaid passageway means, needle valve means in said orifice means forselectively varying said communication between said air pressure chamberand said passageway means, connection means providing communicationbetween said passageway means and said induction passage at the throatof said venturi, and additional connection means providing communicationbetween said chamber means and said induction passage at opposite sidesof the trailing edge of said throttle valve and adjacent thereto whensaid throttle valve is in the closed position; and an outwardly openingreed valve at the outflow end of the induction passage.

2. In a pressure carburetor for an internal combustion engine: a bodyhaving an induction passage therethrough, said induction passageincluding a venturi having a throat; a butterfly throttle valve in saidinduction passage posterior to said venturi; a flexible wet diaphragm;means defining a fuel chamber at one side of said diaphragm and anatmospheric chamber at the other side of said wet diaphragm, saiddiaphragm forming a movable wall between the fuel chamber and saidatmospheric chamber; a dry diaphragm axially aligned with said wetdiaphragm; means defining a signal pressure chamber at one side of saiddry diaphragm and an atmospheric chamber at the other side of said drydiaphragm, said dry diaphragm forming a movable wall between said signalpressure chamber and the last mentioned atmospheric chamber; an operableconnection between said diaphragm; means defining a fuel inlet passagefor said fuel chamher, said inlet passage including a valve chamber; amultisided fuel valve in said valve chamber, said fuel valve controllingthe inflow of fuel to the fuel chamber; a fuel valve control leverpivotally mounted in the fuel chamber and having one end engaging thewet diaphragm and the opposite end operably engaging the fuel valve;spring means urging the lever in a direction to effect closing movementof the fuel valve, said spring means automatically effecting closing ofsaid fuel valve when said engine is not in operation; means defining amain fuel nozzle for discharging fuel into the induction passagedownstream of the throttle valve, said main nozzle being connected withthe fuel chamber and having an air-bleed from atmosphere; air signalpressure means comprising passageway means having one end connected withsaid signal pressure chamber, chamber means, orifice means providing thesole communication between said chamber means and said passageway means,needle valve means in said orifice means for selectively varying saidcommunication between said chamber and said passageway means, connectionmeans providing communication between said passageway means and saidinduction passage at the throat of said venturi, and additionalconnection means providing communication between said chamber means andsaid induction passage at opposite sides of the trailing edge of saidthrottle valve and adjacent thereto when said throttle valve is in theclosed position; and an air-and-fuel mixing chamber at the outlet end ofsaid induction passage, said mixing chamber being enlarged relative tothe portion of said induction passage containing said throttle valve,with said main fuel nozzle being disposed to discharge fuel into saidenlarged mixing chamber.

3. In a pressure carburetor: a body having an induction passagetherethrough with an enlarged air-fuel mixing chamber at the outlet end,said induction passage including a venturi having a throat; a butterflythrottle valve in said induction passage posterior to said venturi; saidmixing chamber being enlarged relative to the portion of said inductionpassage containing said throttle valve; a flexible wet diaphragm; meansdefining a fuel chamber at one side of said diaphragm and an atmosphericchamber at the other side of said wet diaphragm, said diaphragm forminga movable wall between the fuel chamber and said atmospheric chamber; adry diaphragm axially aligned with said wet diaphragm; means defining asignal pressure chamber at one side of said dry diaphragm and anatmospheric chamber at the other side of said dry diaphragm, said drydiaphragm forming a movable wall between said signal pressure chamberand the last mentioned atmospheric chamber; an operable connectionbetween said diaphragm; means defining a fuel inlet passage for saidfuel chamber, said inlet passage including a valve chamber; a fuel valvein said valve chamber, said fuel valve controlling the inflow of fuel tothe fuel chamber; a fuel valve control lever pivotally mounted in thefuel chamber and having one end engaging the wet diaphragm and theopposite end operably engaging the fuel valve; spring means urging thelever in a direction to effect closing movement of the fuel valve; meansdefining a main fuel nozzle for discharging fuel into the enlargedair-fuel mixing chamber of the induction passage, downstream of thethrottle valve, said main nozzle being connected with the fuel chamberand having an air-bleed from atmosphere; and air signal pressure meanscomprising passageway means having one end connected with said signalpressure chamber, chamber means, orifice means providing the solecommunication between said chamber means and said passageway means,needle valve means in said orifice means for selectively varying saidcommunication between said chamber and said passageway means, connectionmeans providing communication between said passageway means and saidinduction passage at the throat of said venturi, and additionalconnection means providing communication between said chamber means andsaid induction passage at opposite sides of the trailing edge of saidthrottle valve and adjacent thereto when said throttle valve is in theclosed position.

4. In a charge forming device for internal combustion engines: meansdefining an induction passage including a venturi having a throat; athrottle valve in said induction passage posterior to said venturi; aflexible wet diaphragm; means defining a fuel chamber at one side ofsaid diaphragm and an atmospheric chamber at the other side of said wetdiaphragm, said diaphragm forming a movable wall between the fuelchamber and said atmospheric chamber; a dry diaphragm axially alignedwith said wet diaphragm; means defining a signal pressure chamber at oneside of said dry diaphragm and an atmospheric chamber at the other sideof said dry diaphragm, said dry diaphragm forming a movable wall betweensaid signal pressure chamber and the last mentioned atmospheric chamber;an operable connection between said diaphragms; means defining a fuelinlet for said fuel chamber; a fuel valve controlling the fiow of fuelinto the fuel chamber; connecting means between the wet diaphragm andsaid fuel valve; yielding means urging the fuel valve in the closingdirection and effecting closing of said valve when the engine is notrunning; means defining an air-bled main fuel nozzle connected with thefuel chamber and discharging fuel into the induction passage downstreamof the throttle valve; and air signal pressure means comprisingpassageway means having one varying said communication between saidchamber and said passageway means, connection means providingcommunication between said passageway means and said 1nduction passageat the throat of said venturi, and additional connection means providingcommunication between said chamber means and said induction passage atopposite sides of the trailing edge of said throttle valve and adjacentthereto when said throttle valve is in the closed position; and anair-and-fuel mixing chamber at the outlet end of said induction passage,said mixing chamber being enlarged relative to the portion of saidinduction passage containing said throttle valve, with said main fuelnozzle being disposed to discharge fuel into said enlarged miningchamber.

References Cited in the file of this patent UNITED STATES PATENTS2,447,791 Barford Aug. 24, 1948 2,722,208 Conroy et a1 Nov. 1, 19552,774,582 Bracke Dec. 18, 1956 2,779,576 Morgenroth Jan. 29, 19572,841,372 Phillips July 1, 1958 FOREIGN PATENTS 577,770 Great BritainMay 30, 1946

4. IN A CHARGE FORMING DEVICE FOR INTERNAL COMBUSTION ENGINES: MEANS DEFINING AN INDUCTION PASSAGE INCLUDING A VENTURI HAVING A THROAT; A TROTTLE VALVE IN SAID INDUCTION PASSAGE POSTERIOR TO SAID VENTURI; A FLEXIBLE WET DIAPHRAGM; MEANS DEFINING A FUEL CHAMBER AT ONE SIDE OF SAID DIAPHRAGM AND AN ATMOSPHERIC CHAMBER AT THE OTHER SIDE OF SAID WET DIAPHRAGM, SAID DIAPHRAGM FORMING A MOVABLE WALL BETWEEN THE FUEL CHAMBER AND SAID ATMOSPHERIC CHAMBER; A DRY DIAPHRAGM AXIALLY ALIGNED WITH SAID SET DIAPHRAGM; MEANS DEFINING A SIGNAL PRESSURE CHAMBER AT ONE SIDE OF SAID DRY DIAPHRAGM AND AN ATMOSPHERIC CHAMBER AT THE OTHER SIDE OF SAID DRY DIAPHRAGM, SAID DRY DIAPHRAGM FORMING A MOVABLE WALL BETWEEN SAID SIGNAL PRESSURE CHAMBER AND THE LAST MENTIONED ATMOSPHERIC CHAMBER; AN OPERABLE CONNECTION BETWEEN SAID DIAPHRAGMS; MEANS DEFINING A FUEL INLET FOR SAID FUEL CHAMBER; A FUEL VALVE CONTROLLING THE FLOW OF FUEL INTO THE FUEL CHAMBER; CONNECTING MEANS BETWEEN THE WET DIAPHRAGM AND SAID FUEL VALVE; YIELDING MEANS URGING THE FUEL VALVE IN THE CLOSING DIRECTION AND EFFECTING CLOSING OF SAID VALVE WHEN THE ENGINE IS NOT RUNNING; MEANS DEFINING AN AIR-BLED MAIN FUEL NOZZLE CONNECTED WITH THE 